This invention relates to the conversion of heat energy from hot fluids into mechanical work, and is particularly concerned with the conversion of heat energy from hot liquids, particularly geothermal brine, to shaft work by means of nozzles, and with apparatus and procedure for this purpose.
Geothermal brines constitute a major store of energy. The temperature of the brines are typically up to about 400.degree. F. and in some cases are at higher temperatures up to about 600.degree. F. Conversion of the internal heat energy of geothermal brine to mechanical or electrical energy is a relatively recent development which has begun to assume considerable importance. Most installations for this purpose have involved the use of equipment designed and built for the commonly employed high temperature energy sources, such as the combustion energy of coal, oil, gas, and the like. The relatively low brine temperature, however, limits the available energy per pound of fluid processed. Further, geothermal brines contain dissolved minerals and salts so that the equipment used for transport and processing present corrosion and/or scaling problems as a result of contact with the geothermal brines. In addition, conventional equipment designed for obtaining energy as by generating electricity, employing convention energy sources such as coal, oil and gas, are complex and involve a high capital cost.
Low temperature, e.g. 300.degree. to 600.degree. F. heat sources such as geothermal brines, have a sufficiently lower theoretical limiting conversion of heat energy to work so that much larger fluid rates are required per unit work output, and thus conventional expansion equipment has a greater fraction of frictional losses as well as capital cost as result of its complexity as compared with a nozzle.
Hence, an energy conversion device for converting the heat energy of geothermal brines to mechanical work is therefore required which is simple, efficient, has a low capital cost and which particularly has a minimum surface in contact with the brine, so as to minimize scaling problems.
A. L. Austin et al in the publication "The Total Flow Concept for Recovery of Energy from Geothermal Hot Brine Deposits," UCRL-51366, April, 1973, have proposed expanding the brine through nozzles arranged to impinge this stream on turbine blades to recover the kinetic energy. This approach has two disadvantages, firstly the nozzles are limited in size and consequently the efficiency will be limited because of losses due to non-acceleration of the liquid droplets and drag on the droplets. Secondly, there will be inefficiencies due to fluid friction associated with recovering the kinetic energy of the nozzle exhaust with the turbine blades.
Another approach of the prior art is the helical screw expander, which is essentially a helical screw compressor operated in reverse. This device is limited substantially to a 3 to 1 pressure expansion ratio. Since recovery of internal energy from, for example, 350.degree. F. geothermal brines requires an expansion ratio of say 20 to 1, several machines of this type in series would be required. The disadvantages of this device are chiefly its complexity, massiveness and cost.
Accordingly, the chief object of the present invention is the design of a device for conversion of the heat energy of hot fluids, particularly geothermal brines, efficiently and employing a simple device, namely the nozzle, requiring low capital investment and having a very small surface area in contact with the hot fluid, and which in contrast to the above Austin et al system, does not require use of a turbine with its high cost and inefficiencies as noted above, to recover the kinetic energy. A further object is the provision of efficient procedure for the conversion of the heat energy of such hot fluids.